Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
The present disclosure relates to a power supply control device including a switching regulator and a linear regulator. The present disclosure also relates to an image forming apparatus and an electronic apparatus including a power supply control device. In particular, the present disclosure relates to a technique for switching between a switching regulator and a linear regulator to serve as a power supply from which power is supplied to loads.
To supply stable power using a power supply control device, a related technique has been proposed in which a switching regulator and a linear regulator are provided. Further, switching between the switching regulator and the linear regulator may provide alternate power supplies. As such, power is supplied to a load in accordance with the output currents of the switching regulator and the linear regulator.
In general, switching regulators reduce a voltage using the switching of, for example, field effect transistors (FETs), whereas linear regulators reduce a voltage using heat generation. Hence, it is known that switching regulators in general have a higher conversion efficiency than linear regulators. However, when the intensity of an output current (consumed current) from a regulator is low, for example, one to ten milliamperes, although the heat loss of a linear regulator is low, the switching loss of a switching regulator is considerably large. Hence, the switching regulator has a lower power conversion efficiency than a linear regulator. As a result, in the related technique, switching from the linear regulator to the switching regulator is performed. As such, power is supplied from a linear regulator to a load when an output current from the regulator is lower than a threshold. Further, power is supplied from a switching regulator to the load when the output current of the regulator is greater than or equal to the threshold, whereby the power conversion efficiencies of the regulators are maintained at high levels.
Printers or multifunction apparatuses have a sleeping time that is much longer than a time for processing jobs. Hence, a reduction in power consumption during a sleeping time is important to reduce the power consumption of printers or multifunction apparatuses. During a sleeping time, processing that consumes a large amount of power, such as image processing, is not performed. As such, power consumption of a control substrate, i.e., current consumption, is small. Hence, it is effective to employ a technique of maintaining high power conversion efficiency even when a consumed current is small as in the power supply control device shown in the related technique described above.
However, considering the power supply control device of the related technique described above, there may be cases in which the power consumption of the linear regulator increases and the temperature of the linear regulator increases to a predetermined temperature. Further, there may be a state where power is supplied to a load from the linear regulator when the output current is below the threshold. In one or more of the cases above, a thermal shut down function operates to protect the linear regulator, whereby the operation of the linear regulator is stopped. When the protection function operates in this manner, although the linear regulator is protected from high temperatures, reactivation of the power supply control device may be required since the regulator has stopped operating.